期刊
MOLECULAR BIOLOGY OF THE CELL
卷 11, 期 3, 页码 915-927出版社
AMER SOC CELL BIOLOGY
DOI: 10.1091/mbc.11.3.915
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- NATIONAL INSTITUTE OF GENERAL MEDICAL SCIENCES [R01GM048624, R01GM035010, R01GM039067, T32GM007464, R37GM035010] Funding Source: NIH RePORTER
- NIGMS NIH HHS [T32 GM007464, GM35010, GM39067, R01 GM039067, R01 GM048624, GM48624, R01 GM035010] Funding Source: Medline
Gcn4, a yeast transcriptional activator that promotes the expression of amino acid and purine biosynthesis genes, is rapidly degraded in rich medium. Here we report that SCFCDC4, a recently characterized protein complex that acts in conjunction with the ubiquitin-conjugating enzyme Cdc34 to degrade cell cycle regulators, is also necessary for the degradation of the transcription factor Gcn4. Degradation of Gcn4 occurs throughout the cell cycle, whereas degradation of the known cell cycle substrates of Cdc34/SCFCDC4 is cell cycle regulated. Gcn4 ubiquitination and degradation are regulated by starvation for amino acids, whereas the degradation of the cell cycle substrates of Cdc34/SCFCDC4 is unaffected by starvation. We further show that unlike the cell cycle substrates of Cdc34/SCFCDC4, which require phosphorylation by the kinase Cdc28, Gcn4 degradation requires the kinase Pho85. We identify the critical target site of Pho85 on Gcn4; a mutation of this site stabilizes the protein. A specific Pho85-Pcl complex that is able to phosphorylate Gcn4 that site is inactive under conditions under which Gcn4 is stable. Thus, Cdc34/SCFCDC4 activity is constitutive, and regulation of the stability of its various substrates occurs at the level of their phosphorylation.
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